The present invention relates to an internal combustion engine cooling system, and, more particularly, relates to an internal combustion engine cooling system which provides either combined cooling for a cylinder head and a cylinder block of the engine, or either partly or totally separated cooling for the cylinder head and the cylinder block, according to operational conditions.
Various considerations arise with regard to the cooling of internal combustion engines which are cooled by the circulation of cooling fluid in passages or jackets formed in the cylinder head and the cylinder block thereof. Some of these considerations relate to the cooling of the cylinder head, and others to the cooling of the cylinder block, and accordingly the old or conventional way of cooling an internal combustion engine, in which the cooling fluid for the cylinder head was always completely mixed with that for the cylinder block, thus ensuring that the cylinder head and the cylinder block were always at substantially the same temperature, has become inadequate.
In more detail, it is important to maximize the thermal efficiency of an internal combustion engine, and in order to do this it is effective to increase the compression ratio or the engine. However, increase of the compression ratio of the engine is limited by the occurrence of so called knocking or pinking, i.e. of detonation caused by compression ignition of the air-fuel mixture within the combustion chambers of the engine. The occurrence of knocking is generally reduced by keeping the cylinder head as cool as possible, and accordingly when the internal combustion engine is being operated, especially in operational conditions in which the occurrence of knocking is a high possibility, such as high rotational speed high engine load operational conditions, it is very important to cool the cylinder head down to as low a temperature as possible.
On the other hand, it is not very advantageous to cool down the cylinder block of the engine to a very low temperature, because in that case the temperature of the lubricating oil contained within the cylinder block, which is strongly influenced by the temperature of the cylinder block, becomes rather low, thus increasing the viscosity of this lubricating oil and causing unacceptably high mechanical energy losses in the engine. Further, because the viscosity of the lubricating oil within the cylinder block when this oil is still cold, i.e. before it has attained operating temperature, is higher than when it has attained operating temperature, therefore of course while this lubricating oil is still cold it causes substantially increased use of fuel by the internal combustion engine, which is very wasteful. Further, if the temperature of the walls of the cylinders of the engine, i.e. the temperature of the bores thereof, becomes low, then the amount of uncombusted hydrocarbons in the exhaust gases emitted by the engine rises, which can cause a serious problem in view of the standards for control of pollution by automobiles, which are becoming more and more severe nowadays.
Another problem that occurs if the temperature of the cylinder block gets low is that wear on the various moving parts of the internal combustion engine, especially bore wear, rises dramatically. In fact, a large proportion of the wear on the bores of an internal combustion engine occurs when the engine is in the non fully warmed up condition, both because the lubricating qualities of the lubricating oil in the engine are not good at low temperatures, and also because the state of mechanical fit to which the parts of the engine are "worn in" or "run in" is appropriate to their physical dimensions when at proper engine operating temperature, and accordingly in the cold condition these parts do not mate together very well. In fact, in view of this matter, it has in the past been an important design goal for internal combustion engines for the moving parts thereof to be warmed up as soon as practicable, or at any rate to be brought to an intermediate temperature higher than a very cold non operating temperature as soon as practicable.
Thus, according to these considerations, it is important to warm up the cylinder block as quickly as possible, when the engine is started from the cold condition, and to keep the cylinder block at quite a high operating temperature thereafter. A difficulty arises in this regard, because during the operation of an internal combustion engine most of the heat which is being generated in the combustion chambers thereof by combustion of air-fuel mixture is in fact communicated not to the cylinder block of the engine, but to the cylinder head thereof. Therefore, transfer of heat from the cylinder head to the cylinder block is very important, especially during the warming up process of the engine. Of course, such heat transfer can take place by the process of heat conduction, since the cylinder head is clamped to the cylinder block, typically however with the interposition of a head gasket which may have a rather low heat conductivity. However, it is desirable to convey heat from the cylinder head to the cylinder block, during engine warmup, more quickly than can be accomplished by this process, and the conventional above described mixing of the cooling fluid within the cylinder head with the cooling fluid in the cylinder block, during engine warmup, is effective for achieving this.
In the prior art, it has been proposed to provide completely independent systems for cooling the cylinder head and for cooling the cylinder block, in order to fulfil the first above described objective of cooling the cylinder head to a low temperature in order to avoid knocking, while keeping the cylinder block warmer, and each of these systems has been equipped with its own fluid pump, conduits, radiator, etc. However, this system does not provide for the above described transfer of heat from the cylinder head to the cylinder block via the cooling fluid, and, since the cylinder block has a considerably large heat capacity, this means that the cylinder block does not warm up quickly from the cold condition, with the ill effects detailed above. Also, the provision of two independent cooling systems increases weight to an unacceptably high extent, and increases manufacturing cost. Further, since in the above described system two independent radiators are used, and the flow amount through each of them is regulated, it is very difficult to use total radiator cooling capacity fully.
Further, there is another effect which is advantageous, and which, in certain circumstances, it is very important to obtain, with regard to the warming up of an internal combustion engine. That is to say, when an internal combustion engine is being operated from a standing or rather cold condition, the fuel in the air-fuel mixture which is being sucked into the combustion chambers of the engine often is not sufficiently vaporized, and accordingly it may well occur that the amount of fuel which is being inhaled into the various cylinders of the internal combustion engine becomes unequal, which may cause irregular and stumbling combustion, which will cause unequal operation of the various cylinders, and a lower level of engine operational performance when the engine is in the cold operational condition, than is available when the engine has been fully warmed up. This, of course, can waste a good deal of fuel, and also can lead to problems concerned with drivability of the internal combustion engine, possibly even involving safety.
Generally, in the prior art, in order to preserve drivability of the vehicle incorporating the internal combustion engine, when said internal combustion engine is in the cold operating condition, it has been practiced to increase the quantity of fuel being provided into the air-fuel mixture being supplied to the combustion chambers of the internal combustion engine, in other words, to richen this air-fuel mixture or to decrease the air/fuel ratio thereof, by the employment of a choke means, in the case of an internal combustion engine equipped with a carburetor, or, in the case of an internal combustion engine equipped with a fuel injection system, to increase the amount of fuel provided in each injection of fuel into the combustion chambers of the engine. If this system of increasing the amount of fuel in the air-fuel mixture provided during cold operation of the internal combustion engine is practiced, then it is possible to escape from the above outlined difficulty with regard to poor performance of the internal combustion engine during cold operating conditions, but the amount of fuel used during warming up of the engine is significantly increased, which is wasteful, and also problems may well arise with regard to the amount of uncombusted hydrocarbons such as HC and CO which are emitted in the exhaust gases of the internal combustion engine at this time.
Another method that has been practiced in the prior art to improve the vaporization of the fuel in the air-fuel mixture which is being supplied to the combustion chambers of the internal combustion engine, in the case of an internal combustion engine which is provided with a carburetor, has been to provide the intake manifold of the internal combustion engine with a riser member which has been heated, either by heat obtained from the exhaust gases of the internal combustion engine, or from heat obtained from an electrical heating system. However, a difficulty arises, in that although on passing this riser member the fuel contained in the air-fuel mixture being sucked into the combustion chambers of the internal combustion engine may well be effectively vaporized, there is a danger of recondensation of part of this fuel, when the air-fuel mixture is actually being sucked into the combustion chambers of the internal combustion engine past the valve ports thereof, when said valve ports are still cold.
Further, in an internal combustion engine provided with a fuel injection system, because it is a desirable feature of conventional construction for the injection of fuel to be performed quite close to the inlet valves of the internal combustion engine, therefore from a point of view of construction it is rather difficult to heat this part of the intake system of the internal combustion engine by the use of heat obtained from the exhaust gases, or from an electrical heater. Therefore, in view of the above described difficulty, especially in cold external operating conditions of the internal combustion engine such as cold climatic conditions, it becomes more important to heat up the material of the cylinder head which surrounds the inlet ports of the combustion chambers thereof, i.e. to heat up the cooling fluid contained within the cylinder head, as quickly as possible, by the heat generated in the combustion chambers thereof. This heating up should proceed until at least the material of the cylinder head which surrounds the inlet ports thereof attains a temperature sufficient to provide a good so called intake mixture vaporization effect. A sufficient such temperature may be around 80.degree. C.
However, it has been difficult, in the forms of art explained above wherein during heating up of the internal combustion engine the cooling fluid within the cylinder head and the cooling fluid within the cylinder block have been mixed, for the cylinder head of the internal combustion engine to be warmed up sufficiently quickly to provide this intake mixture warming up effect, because of the high heat capacity of the cooling fluid contained within the cylinder block, and of the cylinder block. Of course, it will be understood that the real difficulty with regard to the intake mixture warming up effect only occurs during warming up of the internal combustion engine from the very cold condition, or the so called stone cold condition. However, even when the engine is started from a not very cold state, it is of course desirable that the cylinder head should be warmed up as soon as possible in order to effect good vaporization of the fuel in the fuel-air mixture. Once the internal combustion engine has been operating for a few minutes, no further practical considerations exist with regard to this intake mixture warming up effect, since in operation of the internal combustion engine when it is at all warm the parts of the cylinder head around the inlet ports thereof are very warm.